Received-SPF: pass (google.com: domain of linux-kernel+bounces-149021-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Date: Wed, 17 Apr 2024 19:55:38 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Mike Snitzer <msnitzer@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	Damien Le Moal <dlemoal@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Will Deacon <will@kernel.org>, Waiman Long <longman@redhat.com>,
	Guangwu Zhang <guazhang@redhat.com>, dm-devel@lists.linux.dev,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] completion: move blk_wait_io to
 kernel/sched/completion.c
Message-ID: <20240417175538.GP40213@noisy.programming.kicks-ass.net>
References: <31b118f3-bc8d-b18b-c4b9-e57d74a73f@redhat.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <31b118f3-bc8d-b18b-c4b9-e57d74a73f@redhat.com>

On Wed, Apr 17, 2024 at 07:49:17PM +0200, Mikulas Patocka wrote:
> Index: linux-2.6/kernel/sched/completion.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched/completion.c	2024-04-17 19:41:14.000000000 +0200
> +++ linux-2.6/kernel/sched/completion.c	2024-04-17 19:41:14.000000000 +0200
> @@ -290,6 +290,26 @@ wait_for_completion_killable_timeout(str
>  EXPORT_SYMBOL(wait_for_completion_killable_timeout);
>  
>  /**
> + * wait_for_completion_long_io - waits for completion of a task
> + * @x:  holds the state of this particular completion
> + *
> + * This is like wait_for_completion_io, but it doesn't warn if the wait takes
> + * too long.
> + */
> +void wait_for_completion_long_io(struct completion *x)
> +{
> +	/* Prevent hang_check timer from firing at us during very long I/O */
> +	unsigned long timeout = sysctl_hung_task_timeout_secs * HZ / 2;
> +
> +	if (timeout)
> +		while (!wait_for_completion_io_timeout(x, timeout))
> +			;
> +	else
> +		wait_for_completion_io(x);
> +}
> +EXPORT_SYMBOL(wait_for_completion_long_io);

Urgh, why is it a sane thing to circumvent the hang check timer?